Percival Pott, an English surgeon, was the first to report a connection between occupational exposure and cancer. In 1775, he described an unusually high incidence of scrotal cancer among London chimney sweeps and suggested this was due to their exposure to soot and ash. Since then, other coal tar-related cancers have been induced in laboratory animals and found in humans [Kennaway 1995; Kjaerheim 1999]. For example, the PAH benzo(a)pyrene, which was isolated from coal tar in the 1930s, was determined to be carcinogenic when applied to the skin of test animals. In 1947, the relationship between lung cancer and working conditions of gas industry workers and those working with coal tar was established [Kenneway 1995]. An increased incidence of cancers, particularly of the lung, was shown in epidemiologic studies of gas workers [Doll et al. 1965, 1972]. Several epidemiologic studies have shown increased cancer mortality in workers exposed to PAH mixtures. Exposure to other potentially carcinogenic substances often occurred in these studies [Lloyd 1971; Mazumdar et al. 1975; Redmond et al. 1972; Redmond and Strobino 1976; Hammond et al. 1976].